It is known that resin films or resin coated papers of low conductivity become electrostatically charged by friction with dielectric materials and/or contact with electrostatically chargeable transport means, e.g. rollers. The charging occurs particularly easily in a relatively dry atmospheric environment.
Sheets, ribbons and webs made of hydrophobic resin or coated with such resin, e.g. a polyester resin or cellulose triacetate, are commonly used as base materials or supports in recording materials. Such supports are subjected to frictional contact with other elements during the manufacture of the recording materials, e.g. during a coating or cutting stage, and during use, e.g. during the recording of information or (in the case of silver halide photographic materials) during image-processing or projection. Especially in the reeling-up or unfeeling of dry photographic film in a camera or projector high friction may build up, resulting in electrostatic charges that may attract dust or cause sparking. In unprocessed photographic silver halide emulsion materials sparking causes undesirable exposure marks and degrades the image quality.
In order to reduce electrostatic charging of sheets or webs comprising a hydrophobic resin layer or support without impairing their transparency it is known to apply coatings which are formed of or incorporate ionic compounds such as antistatic high molecular weight polymeric compounds having ionic groups at frequent intervals in the polymer chain [ref. e.g. Photographic Emulsion Chemistry, by G. F. Duffin, --The Focal Press--London (1966)--Focal Press Limited,. p. 168, and U.S. Pat. No. 4,301,240]. Examples of polymers that have been used for this purpose include salts of polyacrylic acid, of polystyrene sulphonic acid and copolymers which contain quaternary ammonium groups.
Ionic polymers containing protonated or quaternized amino groups, although being good antistatic agents are often useless in photographic silver halide emulsion materials because of their too high a solubility in water and their fogging activity.
In U.S. Pat. No. 4,301,240 a photographic material is described wherein for the purpose of improving mechanical and electrostatic properties a cross-linked particulate acrylic or methacrylic polymer salt is used in hydrophilic colloid layers such as a gelatin-silver halide emulsion layer or light insensitive gelatin containing layer of a photographic silver halide emulsion layer material.
The advantages of the use of said particulate polymer salts, which are applied as a dispersion (latex), follow from their resistance to diffusion, low swelling power and their property of not influencing the viscosity of gelatinous coating compositions. Said particulate polymer salts remain by their insolubility resistant to diffusion in hydrophilic colloid layers under the conditions of changing pH, e.g. in photographic processing baths.
It has been found experimentally by us that especially the alkaline metal salts of said crosslinked polymers improve the electrical conductivity of a hydrophilic colloid layer but that the corresponding polyvalent metal ion salts, particularly the alkaline earth metal salts and aluminium salts are harmful for that purpose.
Since water washing or rinsing of developed and fixed photographic silver halide emulsion materials proceeds in most cases with natural water containing calcium and magnesium ions stemming from the soil from which tap water is extracted there is a high risk of decreasing the conductivity and consequently of reducing the antistatic character by ion exchange of alkali metal ions of said cross-linked polymer for polyvalent metal ions such as calcium and magnesium ions.